1. Technical Field of the Invention
The present invention relates to the production of functionalized organosilicon compounds. These organosilicon compounds are in particular organosilanes and polyorganosiloxanes (POS), onto which functional radicals, such as, for example, radicals carrying at least one epoxy function, are grafted.
2. Description of Background and/or Related and/or Prior Art
One objective of the functionalization of silicones formed by POS oils is to improve their ability to attach to supports made of paper or the like, of polymer, of glass or of metal. Thus, epoxy-functionalized silicone oils are of advantageous use as anti-adhesive coatings for flexible supports, for example made of paper or of polymer film, or as lubricants.
The grafting of such functional radicals is carried out using precursors which may be of the type of those carrying at least one site of unsaturation, preferably ethylenic unsaturation, capable of reacting with ≡Si—H units belonging to an organohydrosilane and/or a hydrogenated POS. The silicone oils involved are, for example, those of formulae:Me3SiO—(MeHSiO)n—(Me2SiO)m—SiMe3 in which Me=methyl, and n and m are integers or fractions such that 1≦n≦1000 and 0<m≦1000;Me2HSiO—(MeHSiO)o—(Me2SiO)p—SiHMe2 in which o and p are integers or fractions such that 0<o≦1000 and 0<p≦1000.
Many synthons can functionalize polyorganohydrosiloxanes; for example, alkenes, styrenes, allyl alcohols, allyloxy ethers or allylamines are used as synthons.
The hydrosilylation reaction is conventional in the field of the functionalization of silicone compounds, and in particular of POS. It is catalyzed, in homogeneous or heterogeneous phase, by organometallic catalysts, in particular based on transition metals (for example, Karstedt: U.S. Pat. No. 3,775,452 B).
A problem exists which is related to the use of organometallic catalysts such as platinum for the hydrosilylation of ethylenically unsaturated reagents bearing heterocycles (e.g., epoxy), with ≡Si—H units carried by organosilicon compounds such as silicone oils.
In fact, these platinum catalysts for hydrosilylation have the unwanted side effect of promoting opening of the heterocycles, which generates parasitic polymerization/crosslinking involving many heterocyclic functions (in particular epoxides) and which can sometimes result in complete gelling of the reaction medium (formation of gums or of resins). Under these conditions, it is very difficult to obtain final products, namely functionalized organosilicon compounds (silicones), having a completely controlled viscosity. Such a difficulty is particularly harmful for functionalized silicone oils intended for applications such as anti-adhesive coatings.
By way of illustration of this undesirable property that platinum catalysts have of cleaving heterocycles, mention may be made of EP-A-0,415,243, the aim of which is precisely to exploit this property of platinum catalysts for the polymerization of heterocyclic compounds such as epoxy-functional silicones, epoxy-functional acrylic polymers, and also monomers chosen from the group comprising tetrahydrofurans, oxetanes, lactones, spirocarbonates, spiro esters, sulfur-containing cyclic compounds and nitrogenous cyclic compounds.
Various technical propositions have come to the fore in an attempt to solve this problem.
Among them, it is possible to distinguish those involving homogeneous organometallic catalysts and those concerning heterogeneous catalytic systems. As regards the technical propositions in homogeneous phase presented as preventing the opening of the heterocyclic functions, in particular epoxides, of the ethylenic precursors for grafting onto silicones containing ≡SiH units, mention may be made of U.S. Pat. No. 5,258,480 B which discloses a process for preparing epoxy-functional silicones by means of a catalytic complex for hydrosilylation based on rhodium {RhCl3[(CH3(CH2)3)2S]3;PtCl2[(CH3CH2)2S]2} in homogeneous phase and in the presence of a stabilizer consisting of a tertiary amine [CH3(C18H37)2N].
U.S. Pat. No. 5,260,399 B concerns the synthesis of epoxysiloxane monomers and polymers by hydrosilylation in the presence of a homogeneous catalyst comprising a phosphine ligand and a complex based on a transition metal (platinum, palladium, rhodium, iridium, iron or cobalt) and not containing phosphine.
EP-A-0,574,265 concerns a process for preparing an epoxysilicone composition that is crosslinkable by hydrosilylation of an ethylenically unsaturated epoxide, using a silicone containing ≡Si—H units in the presence of a homogeneous catalyst for hydrosilylation containing rhodium of formula:[R4M]+[RhCl3Br]—in which M=P or N and R=C1-18 organic radical.
EP-A-0,574,264 relates to the synthesis of epoxysilicones by hydrosilylation of an ethylenically unsaturated epoxide using a silicone containing ≡Si—H units, in the presence of a homogeneous catalyst of the type quaternary ammonium, phosphonium or arsonium hexahaloplatinate of formula:(R4M)2PtX6in which M=As, P or N; X=halogen and R=C1-30 organic radical.
None of these homogeneous-phase technical propositions provide satisfactory solutions to the technical problem under consideration. In addition, they have the disadvantages of homogeneous-phase reactions. Thus, the functionalized silicone oils obtained from processes using homogeneous catalysis are generally colored, of the order of 120 to 300 hazen; which consequently limits the fields in which their use can be envisioned, in particular in the field of transparent and anti-adhesive films for paper or for transparent films (for example of polyester type). This coloration is generally due to the presence, in the functionalized oils, of metal aggregates or of colloids of nanometric size, derived from the homogeneous catalytic compositions used in the hydrosilylation processes of the prior art. In these cases, the silicone oil requires additional steps of filtration and purification so that it can be usable after crosslinking in the field of transparent films; these supplementary steps make industrial implementation expensive and therefore relatively nonviable in economic terms.
Finally, the catalytic complexes used in these propositions have the disadvantage of being expensive.
In order to be free of the problems associated with homogeneous catalysis, WO-A-97/47677 proposes a heterogeneous organometallic catalysis for obtaining epoxy functionalized silicone oils free of any organometallic residues after filtration. This process for preparing epoxy silicone oils which are weakly colored and low in turbidity by hydrosilylation of hydrogenated POS with unsaturated and epoxidized synthons, in the presence of a metal (platinum) deposited on an inert support, gives relatively satisfactory results in terms of control of the cationic polymerization by opening of the epoxide rings and therefore of the gelling and the viscosity of the final product.
However, this heterogeneous organometallic catalysis can still be perfected, especially in the particular case of 4-vinylcyclohexene epoxide (VCMX).
More recently, U.S. Pat. No. 6,365,696 B disclosed a process for preparing epoxidized POS, according to a platinum-catalyzed process of hydrosilylation between an ethylenically unsaturated epoxide such as VCMX and a hydrogenated POS of the MDD′M type with M=R3—SiO1/2, D=R2—SiO2/2; D′=RH—SiO2/2, in which R=alkyl; in the presence of platinum (chloroplatinic acid solution), of a carboxylic acid salt (sodium propionate) and, optionally, of a promoter for the catalyst, namely an alcohol or a carboxylic acid. The alcohol may be propylene glycol or tetraethylene glycol. Sodium carbonate may be used to treat the VCMX. It should be noted that the process according to that patent is used in the absence of water.